13.6 Performance of the NSSL Experimental Warn-on-Forecast System for Ensembles (NEWS-e) during VORTEX-Southeast

Thursday, 26 January 2017: 11:45 AM
Conference Center: Tahoma 3 (Washington State Convention Center )
Patrick S. Skinner, CIMMS/Univ. of Oklahoma, Norman, OK; and D. M. Wheatley, K. H. Knopfmeier, T. A. Jones, D. C. Dowell, T. T. Ladwig, C. R. Alexander, R. A. Sobash, G. J. Creager, C. K. Potvin, and L. J. Wicker

The goal of the National Oceanic and Atmospheric Administration’s Warn-on-Forecast project is to produce probabilistic, short-term O(1 hr) guidance for severe thunderstorm hazards in the United States.  Working towards this goal, NSSL and the Global Systems Division (GSD) have developed a prototype WRF- and EnKF-based ensemble storm-scale prediction system, which has been run during the winter and spring of 2016.  This system produces twice-hourly updates of 90-min forecasts with 3-km horizontal grid spacing using the 36-member NEWS-e, which is initialized using GSD’s 3-km, experimental High-Resolution Rapid Refresh Ensemble (HRRRE). 

NEWS-e forecasts have regularly produced accurate forecasts of low-level rotation well in advance (>30 min) of tornado development for discrete supercells within highly favorable tornado environments.  However, less is known about NEWS-e forecast performance in more marginal environments typical of cool season tornadoes in the southeastern U.S.  This study examines NEWS-e thunderstorm rotation forecasts for four cool season events in 2015-2016, including for VORTEX-SE intensive operating periods on 31 March and 29 April 2016. 

Each NEWS-e low-level vertical vorticity and updraft helicity forecast is verified against Multi-Radar Multi-Sensor azimuthal wind shear values from the WSR-88D network using an object-based approach.  Additionally, the upstream environment of each forecast rotation object will be extracted from NEWS-e.  This approach allows both storm-scale (e.g. storm size, cold pool interaction) and mesoscale (e.g. conditional instability, vertical wind shear) impacts on forecast accuracy to be assessed across the four cases.

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